OFDM or OFDMA which is based it is a multicarrier modulation scheme which parallelly transmits data by using a multiple orthogonal subcarriers instead of a single carrier having a broad band. It is based on the fact that each subchannel of a narrowband has the flat fading characteristic in the frequency selective fading channel having the very large ISI (Inter-Symbol Interference).
In OFDM, as the symbol is determined on the frequency domain, it is necessary to have an equalizer for frequency domain in order to compensate for the channel distortion of the received symbol. For this, in addition to sending data symbol, the transmitter of the OFDM transmission system transmits the pilot symbol used for the channel estimation for the equalization of data symbol by estimating the characteristics of the channel transmitting a signal.
FIG. 1 is a block diagram that shows the configuration of OFDM receiver of the related art, showing schematically only the unit that restores data from the baseband signal obtained from the received signal.
A burst symbol extracting unit 100 extracts the OFDM symbol from the baseband signal obtained from the received signal by the RF (Radio Frequency) processing unit (not shown). As to the OFDM symbol which is extracted by the burst symbol extracting unit 100, it is applied to an equalizer 108, after the CP (Cyclic Prefix) which is inserted by a CP deleting unit 102 from the transmitter is eliminated and FFT (Fast Fourier Transform) is performed by an FFT unit 104. The equalizer 108 compensates for the channel distortion according to the channel characteristic value which is estimated by a channel estimating unit 106 for the FFT data signal.
After being demodulated in a demodulator 110, the signal compensated the channel distortion performs Viterbi decoding by a decoder 112 and data are restored by the determination of a deciding unit 114. The channel estimating unit 106 performs the channel estimation by using the pilot tone. Pilot tones are arranged between OFDM data tones. In the meantime, when the channel is estimated, the pilot tone is interfered by the pilot tones from the cell of the adjacent base station or other user of the sector. Therefore, the pilot tone interference cancellation technology capable of the exact channel estimation in spite of the interference signal is required.